That’s exactly what two scientists at the University of North Carolina at Chapel Hill have set out to accomplish. Their approach involves using ultrasound from therapeutic instruments commonly found in sports medicine and physical therapy clinics.

Early test results show that they successfully depleted testicular sperm in laboratory rats using the ultrasound method.

Their ongoing effort, aimed at further fine-tuning this technique for maximum effect and safety, could provide men with six months of reliable contraception from a single round of treatment.

The male testis is composed of many tubes called “seminiferous tubules.” As seen in the image above, the tubule from the control testis has many darkly stained germ cell nuclei. Most germ cell nuclei are round; the long, thin nuclei closest to the center of the tubule belong to germ cells called spermatids, which are released as testicular sperm.

In contrast, the ultrasound-treated tubule is completely lacking testicular sperm and has lost almost all immature germ cells, decreasing its overall diameter while greatly increasing the amount of “empty” space in the center of the tubule.

“Once the testis has stopped producing sperm and all ‘sperm reserves’ have been depleted, it is impossible to be fertile,” says James Tsuruta, assistant professor in UNC’s Laboratories for Reproductive Biology.

He says their project “will determine the appropriate ultrasound treatment to temporarily interrupt the supply of testicular sperm yet allow the testis to regenerate itself from the germ cells remaining after treatment.”

The work is being supported by a Grand Challenges Exploration grant from the Bill & Melinda Gates Foundation.